ptlrpc is using rq_xid as matchbits of bulk data, which means it
has to change rq_xid for bulk resend to avoid several bulk data
landing into the same buffer from different resends.

This patch uses one of reserved __u64 of ptlrpc_body to transfer
mbits to peer, matchbits is now separated from xid. With this change,
ptlrpc can keep rq_xid unchanged on resend, it only updates matchbits
for bulk data.

This protocol change is only applied if both sides of connection have
OBD_CONNECT_BULK_MBITS, otherwise, ptlrpc still uses old approach and
update xid while resending bulk.
Signed-off-by: Liang Zhen <liang.zhen@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3534
Reviewed-on: http://review.whamcloud.com/15421Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>